The Interior Department’s inspector general said it dropped a probe into a reported threat by the agency’s head, Ryan Zinke, to Republican Senator Lisa Murkowski of Alaska to harm her state over her opposition to her party’s efforts to repeal Obamacare.

In a letter on Tuesday to two congressmen who called for the probe, Interior Deputy Inspector General Mary Kendall said “further investigation would prove unproductive” after Murkowski and Alaska’s other senator, Republican Dan Sullivan, both declined to be interviewed or provide statements on the matter.

Zinke called Murkowski and Sullivan on July 26, the day after Murkowski’s crucial vote against a motion to begin debate on the healthcare overhaul, the Alaska Dispatch News reported.

The interior secretary warned the two senators that Murkowski’s vote could have negative consequences for energy and land use in Alaska, the newspaper said. Murkowski spokeswoman Karina Peterson confirmed that Zinke had called the senator.

Murkowski did not immediately respond to a request for comment on the inspector general’s decision to drop the investigation.

The Interior Department deals with policies crucial to the state’s economy such as drilling and mining on federal and tribal land and control of wildlife areas.

U.S. Representatives Frank Pallone and Raul Grijalva, the top Democrats on the House committees on energy and natural resources, respectively, had asked the inspector general’s office and the Government Accountability Office for an investigation following the report of the threat.

Zinke suggested he had reconciled with Murkowski, posting a photo on Twitter on Aug. 3 of him drinking Alaska-brand beers with the senator.